Sedimentation apparatus and drive



July 22,1952 R. CHELMINSKI SEDIMENTATION APPARATUS AND DRIVE 5 Sheets-Sheet 1 INVENTOR [Filed Feb. 16, 1946 y 1952 R. CHELMlNSKl 2,604,078

SEDIMENTATION APPARATUS AND DRIVE |Fi1ed Feb. 16, 1946 5 Sheets-Sheet 2 July 22, 1952 [Filed Feb. 16, 1946 R. CHELMINSKI SEDIMENTATION APPARATUS AND DRIVE 5 Sheets-Sheet 3 ATTORN S y 1952 R. CHELMINSKI 2,604,078

SEDIMENTATION APPARATUS AND DRIVE 5 Sheets-Sheet 4' [Filed Feb. 16, 1946 INVENTOR 8mm A/ 0/54 M/A/SK/ Patented July 22 1952 Roman Chelminski, Wilton, Conn., assignor to General American Transportation Corporation, Chicago, 111., a corporation of New York Application February 16, 1946, Serial No. 648,157

1 This invention relates to a driving mechanism for thickeners and other heavy slowly rotating apparatus to which considerable torque must be applied to efiect its turning at the relatively low speed.

An example of the type of mechanisms to which the present invention is particularly applicable is the raking or scraping arms of a thickener or sedimentation tank, such as that shown, for example, in the copending application Serial No. 588,278, filed April 14, 1945, now Patent No.

2,553,958issued May 22, 1951. In apparatus as there'shown the driving mechanism for effecting the rotation of the drumor cage to which the rake or scraper carrying arms are attached is located on a pier at the center of the settling tank and the driving is effected by reductiongear connections from an electric motor to a large ring gear concentric with the drum or cage. Because of the comparatively large diameter of the tanks of such thickeners and therefore the comparatively great length of the arms, high reduction ratios from the motor speed to the speed of rotation of the raking arms are required and special means must be used to equalize the load through several gear trains, or excessively large tooth loads are encountered. In thickeners, for example, in which the tank diameter is 200 feet or more speed reductions of 100,000 to 1 are not uncommon, and torque often is as high as 150,000 foot pounds.

It is obvious-that reductions in speed of this magnitude require elaborate gearing, which is expensive and which occupies considerable space. When a reduction of this magnitude is applied to mechanism such as is employed to drive the scraper or rake-carrying arms of a thickener of thesize above mentioned the space which the reducing gearing occupies upon the central supporting pier leaves little roomfor the provision of a manhole or'other means for obtaining access to other mechanism within the pier.

Even when driving through equalized gearing from at least two diametrically opposed points, 12-inch face gears are often necessary to withstand the stresses on the gear teeth. Not only is it necessary to distribute the driving load so that it is applied in a balanced relation to the axis of the bull. gear,v but it is also necessary that the loads on the teeth of the two driving pinions or other driving means be perfectly equalized.

With the foregoing difficulties in mind, the

present invention aims to provide improved means. for imparting rotary movement, under some or all of the circumstances above recited, to relatively large annular driving gears or bull 2 Claims. (Cl. 121-,117)

wheels such as those employed on thickeners, which means will permit the elimination of substantially all gear trains and which will provide automatically for distribution'of tooth pressures and balanced application of the turning force about the axis of the gear or wheel. I v

More particularly "the-invention aims to provide power transmitting means for-the foregoing I and similar purposes which not only avoids, substantially entirely, the necessity forspeed-reduction gearing, but also avoids the'ne'cessity for differential gearing. i=

With the foregoing and other objects in view.-

the invention uses fluid operated pawls arranged to operate upon a'ratchet ring-gear in suchtimed relation to each other and 'Withsuch balanced pressures, having regardto'their positions about the axis of the gear and any differences in me chanical advantage','that, not only'will they effect continuous slow turning of the ratch'et'wheel or gear, but the application of-the turning torque will be balanced with respect to the axis of' the gear. According to the inventiomthe fluid pressure may be so applied to the driving means that the driving forces exerted upon the ratchet wheel. or gear are equalized through the fiuid.- 7

Other 1 objects and important features pf the invention, to which reference has not specifically been made hereinabove, will appear from the fol-' lowing specification and claims cons'ideredin connection with the accompanying drawings.

In this specification-" and' the accompanying drawings I have shown and described a preferred embodiment of my 'inventiona'nd various modi fication's thereof; but itis to be understood that these are not intended to beexhaustivenor limiting of the invention but, on the contrary, are given for purposes of illustration in order that others skilled in the art may: fully understand the invention and the principles thereof and the manner of applying it'inpracticaluse' so that they may modify and adapt it in various forms, each as may be best suited to theconditions of a particular use. I H I 5 In thev drawings:

Figure 1 is a vertical section of one'half of a sedimentation device orsewage thickener of the type used in sewage disposal plants, the left end of the rake or blade-carryingxarms not being shown in full; I

Figure 2 is an enlarged vertical section, the upper portion of the pier showing, details of the driving mechanism;

Figure 3 is anhorizontal section on the line 3- 3 of Figure 2;

Figure 4-15 an enlarged side section of one of v s the pawl-operating hydraulic or other fluidoperated cylinders and of the piston rod guide and connected pawl; v

Figure is an enlarged section on line 5-5 of Figure 4 of one of the piston rod guides and of the pawl connected to the piston rod;

Figure '6 is a partial sectional view; similar to Figure 2, through a modified embodiment of the invention in which the pawl-operating cylinders are located inside the pier upon which the armcarrying cage or drum is mounted, instead of upon the outside asshown in Figure 2,'an'd in which the pawls act upon a.- downwardly facin ratchet gear;

Figure 7 is a diagrammatic view, showing a control valve partly in section, and. the timing mechanism designed to regulate the speed of'opmounted on the pier extension [6 in such inimner that the piston rod and the trunnion guides have the same inclined relative axis of reciprocal movement to the plane of the ratchet gear 2 as the axes of the cylinders [8, respectively. The trunnions 26 extend through slots 34 in the sides of the guide 36. x

It will be seen that the swinging of the pawl 28 upon the trunnions 26 permits the pawl 28 te ride idly over the ratchet teeth 38 of the ratchet gear 2 on the return stroke of the piston 22 and to drop into operative position again behind the vertical wall of one of the ratchet teeth 38 at the end of the return stroke. Thus on the next thrust stroke of the piston 22 it will engage the ratchet gear 2 through the pawl 28 and will ad- Vance it a distance of one or several ratchet eration of the ratchet gear drive and thecylinders l8, all diagrammatically arranged to show the fluid-circuits; and- Figure 8'is afragmentarywiew'in vertical sec: tion similar to that of Figures-2 and 6, 'butwith different driving cylinders-and control valves embodying. the invention. 'Ihesection of this figure is indicated by 1ine'-88 on-Figure 9. v

Figure 9 is a diagrammatic viewpartly in sectionand partly in plan showing the motor and valve mechanism of- Figure 8.

In the illustrative embodiment. of' the inven tion, the pier l4-,the scraper-arm carrying frame 52. the track 60 and the flanged rollers gor wheels 58 which travel-onthe-track 60 and ar connected to frame 52 .to. support itin'rotatable relation to the .pier: l4 may, be-the same asshown in the copending application of Roman ChelminskL, Otto R. Kuster and Dealy K. I-Iines,- Serial No. 588,278, filedApril 14, 1945. Likewise the frame 52 may have upstandingarms-48 arranged to beengaged by arms or'spokes lfi'of -a central spider, of which the annular ratchet wheel orgear 2' of the present invention forms a part, vthis'ratchet. gear having a downwardly extended annular rib '4- travelling in an annular bearing .bed G and supported in any suitable manner on. an ti-friction bearings 8.,

The bearingbed 6 may be formed-as, or mounted upon, an annular casting l0 havingan inner peripheral flange l2 surrounding a manhole. This casting is supportedupon, andforms a part of the head of, the main pier- M;

A tubularbody l6 secured onthe flange l2 forms an upwardlextension of the pier I4, of reduced diameter, and also provides an access manhole to the interior of" the pier Hi. This body l6 ismade of heavy steelato-serv as a support for-the drivingmechanism, now to be described,

forthe ratchet wheel 2.

As'shown in Figure:2;of thedrawings, in the illustrative embodiment: of the invention the drivingmechanism for-the ratchet gear 2 comprises fiuid cylinders l8- supported: on brackets and; arranged: at; equiangular spacings about the-axis of *thegea'r 2 ,1 eige four cylinders at intervals of 90. It will be noted thatthe-longitu dinal axes of the cylinders l8 are inclined slightly to the plane of the ratchet ,gearx2' at angles suflicient ,to provide clearance for. the cylinders I 8;

and :brackets 20, etc;

Each of: the cylinders-:I8-h'as thereinxa: piston 22 (Figure 4) which is connected by:a.piston.rod 245130 trunnions.-.26:on whichis mounted the U.- shaped pawl 2 8, the. pawlt 2 8 *bei-ng shownv having two arms 30, each of whichxengageslone. of

thectrunnions 26. To .avoid;.undue straini-on the piston rod 24, both the rod 24 andithectrunnions v 26 slide in a: guidestraclcfifiiin the br'acket132,

teeth.

In order that the application of driving force to the ratchet gear 2 may be substantially balanced, about the axis thereof and substantially continuous, there are. preferably provided, as

shown in- Figure 2 of the drawings, a sufiicient number of such pawls 28 and. operating cylinders.

I8 toinsure that at least two-pawls symmetrical- 1y disposed about the axis of rotation. willr operatesimultaneously, toturn the ratchet gear" 2'v While another symmetrically disposed group of! similar pawls are being drawn back by, the re.--

turn strokes of their pistons 22. To insurebal' ancd operation, the cylinders. N3 of eachgroup:

are arranged to operate paw-ls 23 simultaneously and under the same fluid pressure. Since .the

pairs of pistons may overlap-in time ofoperation, i. e., one pair startsits thrust a little. before. the other pair completes its thrust andthusthere is a substantially even flow of power and a steady.

speed of rotation. Such steadiness be-increased-by use of awgreate'r number of -groups-of balanced 'motors, each group operating at different times from the other groups.

To insure the desirednsequence of operationsand. application of balanced forces to oppositesides of the ratchet gear 2 any suitablelvalve timing mechanism may be. provided. InlFigure '7 such a, timing mechanism. whichoperates so-to' control the inputof the operating fiuid'intothe respective ends of the cylinders I8 anditstex haust from the opposite ends that, when two diametrically opposed cylinders lBareoperating,

to advance the pawls 28 and turn the ratchetgear 2 the other two clyinders l8. willbe retracting.

their pawls preparatory for a new thrust-stroke of the stroke of the first'mentioned .pair of pawls;

In this embodiment of-the invention, there-arefour driving pawls 28 and four. pawl-operating;

cylinders I8 having pistons 22:therein. As'h'ere inabove suggested, it is'important to insurethe:

application of balanceddriving torque". to1the ratchet gear 2; so that it'isnot' pushed away.

from its axis but merely turned'about it; To'insure-this there is one set of'valvesA'arrangedzto control the input of they fluid pressure intoiboth' diametrically disposed cylinders I-8"and'the*:ex haust of'the fiuid'therefroi'na and another. set of valves B t is arranged to control the input of theoperatingxfluid into the other'two cylinders-l8 anditsexhaust therefrom. Since the-fluid from these'valv'es is introduced into the two diametri cally. disposed. cylindersfromi the :same manifold;- they willbe under zthesame pressure at all times. Alsoithe pressureofthe operating flu'id supplied' and from the respective sides of the pistons 22 in the cylinders I8: These connections, as shown in Figure 'lcomprise an inlet pipe 12 from a pump or.reservoir (not shown) of fluid under pressure.

Any suitable fluid maybe used, but ordinarily oil is most advantageous. Manifold pipes 14 and 1B serve to carry the fluid to, and to remove it from, the back ends and front ends, respectively, of the upper and lower cylinders 18, as placed on the diagram of Figure 7. Similar manifold pipes 14' and I6 carry the fluid to, and remove it from,

the ends of the right and left cylinders l8 asv placed on Figure '7. Pipes l8 and 80 lead from the valve casing iii to an exhaust sump or low pressure reservoir. These pipes 72, 18 and 89 may be connected to any effective fluid pressure supply system and return, such as are commonly sold and used for various hydraulic motors and control systems.

As herein shown, each of the slide valves 82, 82'- has valve enlargements 84, 8B and 88 thereon making substantially fluid tight fit with'the casinglll, the stem portions between these valve' enlargements permitting flow of fluid between the selected pipes opening into the casing 19 between adjacent enlargements 84, 85 M88. As shown in Figure '7, when the valve 82 is in'its extreme left hand position a "connection is provided between the pipe 16, which is connected to the front end of the cylinder 18, and the pipe 89 leading to the exhaust sump. Thus liquid may be discharged from the cylinders I8 in front of the pistons 22 in the valve set B as they are moved forwardly in the ratchet gear-operating direction. This forward movement is accomplished by the introduction of the pressure liquid from the inlet line 12 through the chamber 98 around the stem portion of valve body 82 and thence through pipe 14 to the cylinders 19 where it enters behind the pistons 22 of the same valve set 13. At this time any flow of liquid from the pipe 14 into the exhaust pipe E8 is shut off by the enlarged valve portion 84.

The valve 82 may be operated directly by a timing mechanism, e. g. from a synchronous electric motor 99 and appropriate gearing 91 and eccentric 9394.

When the valve body 82' is at the right hand limit of its movement as shown we then have the following connections: The inlet pipe '12" is connected to the pipe 16" so that it introduces the pressure liquid into the cylinders [8 in front of the pistons 22 in the valve set A to cause the return stroke thereof.

pipe 18' is connected to the pipe 14 to receive the liquid exhausted from beyond the pistons 22 of the'same valve set A-as they are driven to make their return strokes by the liquid introduced in front of them, through connections 12' to the pipe 16.

-Thecontrol of the operation of the two valve mechanisms A and B shown in Figure '7, to insure the proper relative timing thereof, may be B is arranged to control the operation of those, cylinders which are marked B .on Figure '7 of the drawings; To insure operation of these valves in proper timedrelation to each other the valve 82 is connected to a stem 99 passing through a stufling box 9l. The stem 90 is in turn connected by a clevis and pin connection 92 to an eccentric strap 93 surrounding an eccentric 94-on a shaft 96 having thereon a worm wheel 91 which may be driven by a worm (not shown) atany desired uniform speed, e. g., by a synchronous.

motor .99. A cam designed to give a long power stroke and quick return, with consequent over- The exhaust pipe 89' is shut off by the valve portion 88 while the exhaust lapping of power strokes of cylinders A and B, maybe used instead of eccentric 93. It will-be evident that many cam forms can be used.

The valve 82' of the valve mechanism'A is'similarly connected to a'rod' 99 passing through a stuffing box 9|. The rod is in turn connected by a yoke and pin connection 92 to the strap '93 on an eccentric "94 on the same shaft 96 as the eccentric 94 but turned on the shaft 96 with respect to the eccentric 94. It will thus be seen that, as the shaft 96 is turned by the worm and worm gear drive connection, the valve mechanism A will control its two cylinders A (Figure '7) to operate their pawls to turn the ratchet gear 2" when the cylinders B-under control of the valve mechanism'B have completed their thrust stroke. The two groups of cylinders 18 thus alternate and there will thus be a substantially continuous being located upon'the reduced extension IE5 or the pier I4, is shown as located within the pier Ma. In Figure 6 the annular gear Z is shown as having downwardly facing ratchet ,teethfBBa on an annular flange J96 overhanging'the upper end I94 of the pier 14a. A depending rib 4a received a bearing ring 6a carried by brackets or a flange] l2 on the upper end IM of the pier Ma. Suitable antifriction bearings 8a maybe provided in the ring 6a upon which the rib 4a rests.

Inthis form of the invention the cylinders I8a are carried upon inwardly extending brackets 2911 on the inner wall of the pier Ma and the pawls 28a, operating from the pistons 22a by connections throughthe piston rods 24a similar to the connections between pawls 28 and piston rods 24 hereinabove described, are held in operative relation to the ratchet teeth 3 8a, against the tendency of gravity to move them away from the teeth 38a, by counter weights 29a.

The equiangular, spacing of the cylinders 18a about the axis of the gear 2a and the timing of the operations of the various pawls 28d will be the same otherwise as'it is in the form of the invention hereinabove described.

In the embodiment shown and described, the-operation of thepawls 28 has been described as brought about by cylin ders I8 having fluid-operated pistons therein which arefluid-operated in both directions. Although this is the more advantageous arrangement, ,and fluid-operation in the power applyin direction is practically essential, it will be under.- stood the return stroke of the piston is not confined to fluid operation, but may be, e.;g-.,-by means of a spring. Y

An alternative valve arrangement is shown in Figures 8 and 9. In Figure 8 the bull ring 2 rotates in the bearing 6 and drives the scraper frame f the invention herein urea "A bracket r20: secured to the side of the' neck Itbc'arries agear b'o'x' I22 with lower pin-' ion I23 meshi'ng witha -ring gear I24 secured to thebull ring 2 'as sh'own.. Above the gear box I22-anddr'iven by it, isr a rotary valve mechanism I 2 6. This valve. mechanism. I2 6 consists of a 031- lindrical' shell and rotor, the shell having a pres-- sure-inletport I2'I':at an uppermost level; an exhau'st port-{1:43; at a lowermost level and, on an intermediate level, a connection Ir'2 8 to an -auxi1-" iary' valve I30 for the modified ratchet motors I8b;- The'rotor- I4 'I has passages drilled through it tointerconnect inlet I21 01% the exhaust I43 with*the port I28. The auxiliary valve motor I33 isconnected to the port I28 in the rotary valve housing? to; op erate its piston I34- connected to main valveslide I32".-

The rotaryvalve I 26 isprovided, in additionto the auxiliary valve connection I28 withpressure inlet-andexhaust ports I21 and I43. As shown in Figure 8, these are on levels respectively higher and'lower than the auxiliary valve connection I28; the latter being connected to a port withinthe valve housing bywhich it may communicate withthe ports I45-and- Mfi respectively; (Figure-9) in the rotary valve coret The pressure inlet con: nection, I=21 is o n;the same levelas-the inlet end of-portil45 in the valve core andithe outlet of port-I4 5 ispnthe levelof the port I28-,-and thereforeaifords communication between the pressure inletand the-auxiliary valve connection I28 when the core is inthe-proper angular position just beyond'that shown at the right in Figure 9; Port I46 has its outlet end on the'same level as the exhaust port I43 and its inlet' end' on the level-' ofp'ort' I2 8. It" therefore makes connection between the auxiliaryvalve connection- I28 andthe exhaust'port'when the valve core is in the proper angularfiposition; just before that shown at the left ofFig'urie9; n s

The charnherbehirid the sli'iall iston I3 5- is; connectedto' a' 'con'starit pressureiiiletline I36" which may 'be at' the same' pressure'asthat supplied through the rotary. valve I 26 fr'onipo'rtf I43.

The valve motor I33" operates" when this'pres= sure is introduced through. [23' into'- the'end' of the cylinder because of 'the greater area exposed on" the end of theipiston" .I 3' I"as compared'with' the annularar'ea'; around the pistonrod on theopposite swear the piston. The area of the piston rodisat the exhaust pressure, since the opposite endof themairi valvesli'd'e' is always exposed-to the exhaust line" I 4' I:

The line I385 connects this main valv'e' with theends of theratchet-motorcylinders IBb-dif ametrically opposite positions-on" thebull ring 25 The relation between'the inlet a'nd'theo'utlet port's I36 an'dl I38 is such that inthe position shown they are-separated by the valve' slide- I 32;-

whereas when th slide is moved-to the opposite end of the cylinder they are connectedthrough-- thereduceddiameter prtionof the slide:

- Exhaust port's -I40 and- I4I are provided' tb relieve the pressure between the slide valve andea'ch end ofits cylinder. These ma be Open to the oi atmosphere butpreferalfly are provided with connections td an hydraulicreservoir in order" to drai-ii h'aek any" liquid which may leak back past thevalve' slidel" 7 r The piston-rod 2 4b forpiston '22 b in thei'r'aitohe't motor cylinder'i'sshown-relatively large so that": only a small volume remains within thecylinder around-'the piston rod 241) tobefille'd by 'the' fluid under pressureadmitted through port ms which, in this cas'epis'. constantly open to' the"fiuid?pres- I sui'e source in thesa'me manner as port" I36 of ning' the next;

twee'n the'farea on th'e-end of the-piston and'theannularareaexposed to the pressure on' the opposite side ofthepiston; 7

When pressure-is admitted through the port I38 inthe auxiliary valveythepiston 22b will be driven forwardand liquidexpelled through the portIfitasthe-operation of the'motor progresses;-

At-the'end of this stroke the auxiliary valve is reversed; sothat port I38 is opened totherelief" port 'I 40-, the pressure-liquid escapes from the endof cylinder I8b and liquid under pressure enters through port- I48 to drive the piston back andthereby retractthepawl for a new power strolge. As the bull ring 2 is rotated, thepinion I23 is driven fromring gear I24 and the valve core I4! is rotated; with such gear ratio in; the transmissionIZZ-that durinjgthe forward stroke of the pawltheport I45 rotates from'the position shown at the right in Figure' Q- to a position in which the port I46 is aligned'bet'ween the valve' port I 28- and exhaustport I43.

When this latter condition occu s; the valve operatingcylinder 438 is'connected'through the port I28 and the port I4 'li tothe reliefport whereupon'the piston If3 l-isnioved by the pressure-from the port I36 exerted on the bacli' -of' piston I34, and thereby the port I38'is connected to therelief port I30 causing retractionof the main operating pistons 2%, as previously debed; I c

While this occurs theother pair of ratchet motors continue to rotate the bull ring 2} and therefore the valvecore I41 continues to rotate untilthe passage I Qifisagain aligned be'tween theportsIZT and I 28. Liquid u'nder pressure thenit acts-on piston I34 to'rn'0ve the valve-slide I32: to the right and thereby connectingthe pressure.

inlet I36; through connection I33 to the ratchet motors 22b of the diametrically opposite pair,

Since it is desirable to have a relatively long operatingstrolie and a quick retracting-stroke, the por-t- I46 is angular-lyspaced fromthe port over 'a" period equalto about 330 of the rotation otthe 'rotary valve, whereas the" retracting-action will-becorhpleteddn the remaining'30 of the r'o-' tat'ion:

The. operation of the 'opposite lc'ylinders is shown-in Figure 9 'a's controlled bya separately drivenrotary'valve'identical: with I4"'I but 180 out of phase. achieved=bymerely having additional ports and passagesdn an extended rotorand cylindricalcasing 'with angular relation such; for example,- as 1 lS"ST1OWh between those oi" the" separate valve" mechanisms inFigureQ: I If these are; as"=shown,- 180? In practice, some economy is outof phase' the- 5; retraction of 'thepistons controlled'byone valve" will occur during the full power stroke of other cylinders controlled by the other valve mechanism; and thus at all times there will be a power stroke operating. If desired with a suitable even number of ratchet motors I81) and a suitable number of valve mechanisms I26, the timing may be set so that one pair of cylinders takes hold precisely at the time another pair drops out of action and a third pair takes hold precisely at the time that the first drops out of action and so on, utilizing the maximum period of the power stroke of each cylinder, but giving a total power flow which remains substantially constant. However, any desired numbers of valves and ratchet motors may be used.

The gear ratio in transmission I22 is, of course, such that the rotor I4'I moves from the position in which passage I45 is aligned between I21 and I28 to the position in which passage I46 connects I28 with I43 while the pawl 28 and piston MD are making a normal power stroke.

Speed control in this type of drive may be by controlling operation of a pump connected through a direct line and manifold to the inlet ports I21, I36, I40, MI and I48, or by a throttle valve on a line from a pressure reservoir. These conventional units are omitted from the drawings to avoid complication and confusion as their existence and relation will be readily understood by those skilled in the art without such illustration.

As will be apparent also, the proportions of valves, motor cylinders, pistons, etc., are distorted in the diagrammatic showing of Figures 8 and 9, as otherwise these parts would be too.

small for easy reading of the drawing or the complete drive unit would become too large to show on a single drawing.

What I claim is:

1. A rotational drive for heavy slow moving apparatus which comprises a bull gear, a plurality of groups of reciprocating fluid pressure motors having fluid pressure supply valves operatively associated therewith, said motors being positioned adjacent said gear with the motors of each group arranged in balanced relation about the axis of said gear, means for transmitting force from each motor as a turning moment to said gear, the throw of said motor being so small relative to the radius of the gear that said turning moment remains substantially constant while the fluid pressure supply valves are open, and means including control valves and manifolds for supplying fluid under pressure to said motors, the motors of each group being supplied with fluid pressure from a common source, whereby driving force is distributed simultaneously through the motors of the group to their several parts of the bull gear, and valve timing means controlling operation of said valves so that fluid pressure is supplied successively to the said groups of motors respectively, whereby one group exerts its turning moment on the gear while the motors of another group are in their retractile stroke and thus a substantially continuous turning movement is imparted to said gear.

2. A rotational drive for heavy slow moving apparatus which comprises a bull, gear, a plurality of groups of fluid pressure motors having fluid pressure supply valves operatively associated therewith, said motors being positioned adjacent said gear with the motors of each group arranged in balanced relation about the axis of said gear, means for transmitting force from each motor as a turning moment to said gear, the throw of said motor being so small relative to the radius of the gear that said turning moment remains substantially constant while the fluid pressure supply valves are open, means including control valves and-manifolds for supplying fluid under pressure to all said motors of said groups respectively, a common source of fluid pressure connected to said manifold for supplying motive force toall the motors of each group, whereby driving force is distributed simultaneously through the motors of the group to their several parts of the bull gear.

ROMAN CI-IELMINSKI.

REFERENCES CITED The followingmeferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 684,713 Payton Oct. 15, 1901 933,637 Farrell Sept. 7, 1909 1,939,887 Ferris et al. Dec. 19, 1933 1,985,589 Ter Meer Dec. 25, 1934 1,988,749 Reswick' Jan. 22, 1935 2,077,744 Cuno et a1. Apr. 20, 1937 

